Preconcentration and speciation of arsenic in water specimens by the combination of solidification of floating drop microextraction and electrothermal atomic absorption spectrometry.

A simple solidification of floating drop microextraction procedure for preconcentration and speciation of trace amounts of As(III) and As(V) in water samples has been proposed prior to electrothermal atomic absorption spectrometry (ETAAS). In this method, a free microdroplet of organic solvent is floated on the surface of aqueous solution while being agitated by a stirring bar placed on the bottom of the sample vial. The determination of As(III) was achieved by selective formation of the As(III)-pyrrolidine dithiocarbamate complex in the presence of 0.1M HCl while As(V) forms a weak complex with the ligand in the same pH conditions. Total inorganic As(III, V) was extracted similarly after reduction of As(V) to As(III) with potassium iodide and sodium thiosulfate and As(V) concentration was calculated by difference. Pd(NO(3))(2) was used as a chemical modifier in ETAAS. Some important extraction parameters such as the type of organic solvent, solvent volume, sample stirring rate, sample solution temperature, salt addition and the exposure time on the extraction recovery were investigated and optimized. Under the optimized extraction conditions, the detection limit of 9.2 pg mL(-1) and suitable precision (RSD<8.6%), along with enhancement factor of 1000 for As were achieved. The developed method was applied successfully to speciation of As(III), As(V) and determination of the total amount of As in water samples.

Comparison of solidification of floating drop and homogenous liquid-liquid microextractions for the extraction of two plasticizers from the water kept in PET-bottles.

Two approaches based on solidification of floating drop microextraction (SFDME) and homogenous liquid-liquid microextraction (HLLE) were compared for the extraction and preconcentration of di-(2-ethylhexyl) phthalate (DEHP) and di-(2-ethylhexyl) adipate (DEHA) from the mineral water samples. In SFDME, a floated drop of the mixture of acetophenone/1-undecanol (1:8) was exposed on the surface of the aqueous solution and extraction was permitted to occur. In HLLE, a homogenous ternary solvent system was used by water/methanol/chloroform and the phase separation phenomenon occurred by salt addition. Under the optimal conditions, the LODs for the two target plasticizers (DEHA and DEHP), obtained by SFDME-GC-FID and HLLE-GC-FID, were ranged from 0.03 to 0.01 microg/L and 0.02 to 0.01 microg/L, respectively. HLLE provided higher preconcentration factors (472.5- and 551.2-fold) within the shorter extraction time as well as better RSDs (4.5-6.9%). While, in SFDME, high preconcentration factors in the range of 162-198 and good RSDs in the range of 5.2-9.6% were obtained. Both methods were applied for the analysis of two plasticizers in different water samples and two target plasticizers were found in the bottled mineral water after the expiring time and the boiling water was exposed to a polyethylene vial.

Development of liquid phase microextraction method based on solidification of floated organic drop for extraction and preconcentration of organochlorine pesticides in water samples.

A simple and efficient liquid-phase microextraction (LPME) in conjunction with gas chromatography-electron capture detector (GC-ECD) has been developed for extraction and determination of 11 organochlorine pesticides (OCPs) from water samples. In this technique a microdrop of 1-dodecanol containing pentachloronitrobenzene (internal standard) is delivered to the surface of an aqueous sample while being agitated by a stirring bar in the bulk of solution. Following completion of extraction, the sample vial was cooled by putting it into an ice bath for 5 min. Finally 2 muL of the drop was injected into the GC for analysis. Factors relevant to the extraction efficiency were studied and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 65 degrees C; sodium chloride concentration: 0.25 M; microdrop and sample volumes: 8 muL and 20 mL respectively; the stirring rate: 750 rpm and the extraction time: 30 min), figures of merit of the proposed method were evaluated. The detection limits of the method were in the range of 7-19 ngL(-1) and the RSD% for analysis of 2 mugL(-1) of OCPs was below 7.2% (n=5). A good linearity (r(2)> or =0.993) and a relatively broad dynamic linear range (25-2000 ngL(-1)) were obtained. After 30 min of extraction, preconcentration factors were in the range of 708-1337 for different organochlorine pesticides and the relative errors ranged from -10.1 to 10.9%. Finally the proposed method was successfully utilized for preconcentration and determination of OCPs in different real samples.

Extraction and determination of organophosphorus pesticides in water samples by a new liquid phase microextraction-gas chromatography-flame photometric detection.

A rapid, sensitive and efficient liquid phase microextraction (LPME) method was developed to determine trace concentrations of some organophosphorus pesticides in water samples. This method combines liquid phase microextraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little organic solvent consumption. It involves exposing a floated drop of an organic solvent on the surface of aqueous solution in a sealed vial. Experimental parameters which control the performance of LPME such as type of organic solvent, organic solvent and sample volumes, sample stirring rate, sample solution temperature, salt addition and exposure time were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by the water samples spiked with organophosphorus pesticides. Using optimum extraction conditions, very low detection limits (0.01-0.04mugL(-1)) and good linearities (0.9983

A new liquid-phase microextraction method based on solidification of floating organic drop.

In the present study, a new and versatile liquid-phase microextraction method is described. This method requires very simple and cheap apparatus and also a small amount of organic solvent. Eight microliters of 1-undecanol was delivered to the surface of solution containing analytes and solution was stirred for a desired time. Then sample vial was cooled by inserting it into an ice bath for 5 min. The solidified 1-undecanol was transferred into a suitable vial and immediately melted; then, 2 microL of it was injected into a gas chromatograph for analysis. Some polycyclic aromatic hydrocarbons (PAHs) were used as model compounds for developing and evaluating of the method performance. Analysis was carried out by gas chromatography/flame ionization detection (GC/FID). Several factors influencing the microextraction efficiency, such as the nature and volume of organic solvent, the temperature and volume of sample solution, stirring rate and extraction time were investigated and optimized. The applicability of the technique was evaluated by determination of trace amounts of PAHs in environmental samples. Under the optimized conditions, the detection limits (LOD) of the method were in the range of 0.07-1.67 microg L(-1) and relative standard deviations (R.S.D.) for 10 microg L(-1) PAHs were <7%. A good linearity (r(2)>0.995) in a calibration range of 0.25-300.00 microg L(-1) was obtained. After 30 min extraction duration, enrichment factors were in the range of 594-1940. Finally, the proposed method was applied to the determination of trace amounts of PAHs in several real water samples, and satisfactory results were resulted. Since very simple devices were used, this new technique is affordable, efficient, and convenient for extraction and determination of low concentrations of PAHs in water samples.